As an internal combustion engine for a vehicle including an automobile, a type having a direct injector for injecting fuel into a cylinder and a port injector for injecting fuel into an intake port is known.
For fuel injection from the direct injector, a target fuel injection amount of the fuel injection is first determined. The target fuel injection amount is set using the requested fuel injection amount for an internal combustion engine as a whole and the dual-injection ratio between the direct injector and the port injector necessary for reaching the requested fuel injection amount. The requested fuel injection amount and the dual-injection ratio are determined based on the engine operating state including the engine speed and the engine load. Then, the direct injector is actuated to achieve the target fuel injection amount such that at least some of the fuel amount corresponding to the requested fuel injection amount is injected by the fuel injection from the direct injector.
As described in Patent Document 1, the fuel injection from the direct injector for achieving the target fuel injection amount may be performed in a divided manner in a plurality of shots. Specifically, as described in the document, the fuel injection from the direct injector may be carried out in a divided manner in a shot corresponding to the early stage of the intake stroke and a shot corresponding to the late stage of the intake stroke or in a divided manner in a shot corresponding to the early stage of the intake stroke and a shot corresponding to the compression stroke or in a divided manner in a shot corresponding to the early stage of the intake stroke, a shot corresponding to the late stage of the intake stroke, and a shot corresponding to the compression stroke. In these cases, the aforementioned target fuel injection amount for the full amount of the fuel injected from the direct injector is divided into target fuel injection amounts for respective fuel injection shots in correspondence with a predetermined ratio. The direct injector is then actuated such that the respective target fuel injection amounts are achieved.
Specifically, in the fuel injection from the direct injector, the fuel injection in the compression stroke, the fuel injection in the late stage of the intake stroke, and the fuel injection in the early stage of the intake stroke bring about desirable engine operation, as will be described in the items [1], [2], and [3] below.
[1] The fuel injection in the compression stroke is characterized in that air streams in a cylinder are easily collected near an ignition plug and thus achieves desirable ignition of the fuel in the cylinder to increase the fuel combustion speed. [2] The fuel injection in the late stage of the intake stroke intensifies the air streams in the cylinder through injected fuel to achieve desirable fuel combustion, when the piston movement speed decreases and thus reduces air stream generation in the cylinder. [3] The fuel injection in the early stage of the intake stroke allows the injected fuel to adhere directly to the piston top and thus cools the piston top using latent heat of vaporization produced by the fuel and suppresses the occurrence of knocking in the engine.